Referring to FIG. 1, a conventional 4-way radio frequency (RF) power amplifier circuit includes three Wilkinson power dividers 11, 12, six power amplification circuits 15, 16, and three Wilkinson power combiners 13, 14.
Further referring to FIG. 2, the Wilkinson power divider 11 includes an input line 111 receiving an RF input signal (Pi) that has a wavelength of λ, two quarter wave lines 112, 113, a resistor 116, and two output lines 114, 115. An input impedance (Z111) seen into the input line 111 is equal to an output impedance (Z114, Z114) seen into each of the output lines 114, 115, where Z0=50 ohms. The quarter wave lines 112, 113 have a length of λ/4 and are Y-shaped, thereby dividing the RF input signal (Pi) into two first RF division signals (P1). The output lines 114, 115 are respectively coupled to the quarter wave lines 112, 113 to output the first RF division signals (P1). The resistor 116 is coupled between the quarter wave lines 112, 113 to enhance isolation and prevent the first RF division signals (P1) from interfering with each other.
The power amplification circuits 15 respectively receive the first RF division signals (P1), perform power amplification on the first RF division signals (P1), and output first RF amplification signals (P2) to the Wilkinson power dividers 12.
Similarly, the Wilkinson power dividers 12, which are configured to be the same as the Wilkinson power divider 11, divide the first RF amplification signals (P2) into four second RF division signals (P3), and the power amplification circuits 16 perform power amplification on the second RF division signals (P3), and output four second RF amplification signals (P4).
The Wilkinson power combiners 13, 14 are configured to be the same as the Wilkinson power divider 11, but are used in a reverse way. Accordingly, taken the upper one of the Wilkinson power combiner 13 as an example, the input impedances (Z131, Z132) thereof are both 50 ohms, and an output impedance thereof (Z133) is also 50 ohms. Each of the Wilkinson power combiners 13 receives and combines two of the second RF amplification signals (P4) into an RF combination signal (P5). Then, the Wilkinson power combiner 14 receives and combines the first RF combination signals (P5) into an RF output signal (Po).
Such a conventional RF power amplifier circuit has at least the following drawbacks:
1. Large chip area is required: Since each of the Wilkinson power dividers 11, 12 and the Wilkinson power combiners 13, 14 has the quarter wave lines each having a length of λ/4 (i.e., an electrical length of 90°), the overall layout length would be approximately 4×λ/4, which may occupy a large chip area.
2. Power gain and power-added efficiency (PAE) are reduced: The large area of the Wilkinson power dividers 11, 12 and the Wilkinson power combiners 13, 14 may result in higher signal loss, so the power gain between the RF output signal (Po) and the RF input signal (Pi) is reduced, further reducing the PAE.